Justin Timberlake and Christina Aguilera, the charismatic co-headliners behind the “Justified and Stripped” tour, share much in common. Both former teen pop stars reinvigorated their careers by tapping into black music traditions such as hip-hop and soul. And, as their performances at Philips Arena on Saturday night proved, both exhibit a degree of polish that belies their youth.

Aguilera hit the stage first, belting out her jittery, rap-influenced jam “Dirrty.” Though her recent (and relatively slight) weight gain has made headlines, she fearlessly flaunted her new voluptuousness in a number of body-hugging, belly-baring outfits.

Indeed, Aguilera’s set suggested that she lives by three mottoes: Flesh is made to be revealed. Nothing is best left unsaid. And lessons are most interesting when learned the hard way.

Before singing the lullaby-like “Walk Away,” she asked, “What do you do when something’s bad for you and you still can’t let go?”

And, while introducing the rock-edged “Fighter,” she addressed naysayers: “I want to thank you because you made me that much stronger.”

Vocally, Aguilera alternated between sounding light and fluttery and coming across gutsy and strong. She exhibited so much power that, given today’s standards, it’s almost shocking that she’s successful.

This was especially apparent during her rousing finale, “Beautiful.” “I am beautiful no matter what they say,” the singer roared on the spare, piano-driven ballad that seemed like both an all-purpose anthem and a deeply personal mantra.

Where Aguilera offered empowerment, Timberlake sold seduction. “Is there anybody out there tonight who would be my girlfriend,” he asked the packed house, which included his rumored new gal pal, Cameron Diaz.

Timberlake’s stage set-up resembled a red-upholstered after-hours spot. It looked like the kind of place where bonds of love and lust are easily forged and broken. And Timberlake had songs for both circumstances.

“Gonna have you naked by the end of this song,” he teased on the playful “Rock Your Body.” Soon, however, his tone turned dark when he delivered the bitter kiss-off “Cry Me a River.”

But even at his most mean-spirited, Timberlake exudes a sensitivity that sets him apart from the bad-boy rockers and thuggish rappers who compete with him on the charts. When he sang, “There [are] the good guys and also heartbreak crooks,” there was no doubt which one he was.